Heretofore, the herein concerned actuators, as employed, for typical example, with single port globe values in 1-6 in. control applications, have been beset by these following problems, all uniquely solved by this invention:
1. Non-achieving of wanted or required high stem or seating force, with no more than normal plant air system or controller output supply pressure, and without excessive increase in diaphram size.
2. Non-providing of degree of actuator stiffness required for valve stability, i.e., of positive rate of actuator-induced stem force change (with actuator stroke) exceeding a negative rate of flowing-medium-induced stem force change (with actuator stroke).
3. Compression spring differentiation for, or more generally non-convertability as between, normally closed and normally open operation.
4. Non-standardization of spring location and size.
5. Varying mountings and constructions of auxiliary hand wheels.